1. Field of the Invention
The present invention relates to a protective film forming method and, more specifically, to a method for forming a thin protective film on a surface of a protection target.
2. Description of the Related Art
Recently, in order to implement size-reduction and large capacity, there has been a rapid advancement in increasing the recording density of magnetic disk devices. Accordingly, it is required to decrease distance between a magnetic head slider and a magnetic disk, i.e., to decrease floating amount of the magnetic head slider further with respect to the magnetic disk.
In the meantime, a decrease in the floating amount of the magnetic head slider with respect to the magnetic disk may increase a chance for the magnetic head slider to be in contact or to be collided with a magnetic head face that is being rotated at a high speed. Thus, it is necessary to form a protective film on a floating face of the magnetic head slider. Further, it is necessary for the protective film to have a high sliding characteristic (low friction characteristic) and abrasion resistance since it may come in contact with the magnetic disk face. Furthermore, for increasing the recording density, it is necessary to form a thickness of the protective film to be extremely thin in order to narrow the distance between a magnetic head element part and the magnetic disk. Moreover, the magnetic head element part comprises a magnetic recording element and a magnetoresistive element working as a reproducing element. Each of those elements is formed with a magnetic material that is easily corroded, so that the protective film is also required to have a function of preventing corrosion of the magnetic materials.
Now, a magnetic head slider protective film forming method employed conventionally will be described by referring to FIG. 1. As shown in a flowchart of FIG. 1, a protective film of a magnetic head slider is formed by going through a step of cleaning a surface of a protection target (magnetic head slider) in a bar block that includes a plurality of magnetic head sliders in a connected state (step S101), a step of forming a base film that contains silicon as a main component (step S102), and a step of forming a diamond-like carbon film (DLC) thereon (step S103). That is, the protective film of the magnetic head slider formed in this manner is constituted with a double-layered film that includes the base film made of a silicon film or a silicon oxide film, and the DLC film formed thereon.
Then, the magnetic head slider manufactured through the above-described steps is required to pass various kinds of corrosion tests so that the quality thereof can be maintained. Typical examples of the corrosion tests are an acid dipping test depicted in Patent Document 1 and a hot-and-humid test depicted in Patent Document 2.    Patent Document 1: Japanese Unexamined Patent Publication 2006-107673    Patent Document 2: Japanese Unexamined Patent Publication 2007-26506    Patent Document 3: Japanese Unexamined Patent Publication 2001-343227
However, when thickness of the protective film formed through the above-described steps, i.e., the protective film constituted with a double-layered film, is tried to be made thinner, it is difficult for such protective film to pass the corrosion tests mentioned above with the film thickness of less than 2 nm, for example. Therefore, the protective film of the above-described structure cannot be made thinner because of its corrosion resistance, so that it is not possible to achieve high recording density. Inversely, when the film of such protective film is thinned, the corrosion resistance is deteriorated. This results in deteriorating the quality of the magnetic head slider.
Further, as shown in FIG. 2, a protective film in a structure disclosed in Patent Document 2 is formed by going through a step of cleaning a surface of a protection target (magnetic head slider) (step S201), a step of forming a base film that contains silicon as a main component (step S202), a step of forming a diamond-like carbon film (DLC) thereon (step S203), and a step of thinning the thickness of the diamond-like carbon film by etching (step S204). Patent Document 2 discloses that this makes it possible for the protective film with the film thickness of less than 2 nm to pass the hot-and-humid test mentioned above. However, the protective film disclosed in Patent Document 2 is the double-layered film as in the case of Patent Document 1, so that it is difficult for this protective film to pass the acid dipping test that has more strict conditions. Therefore, it is still impossible with the protective film of Patent Document 2 to improve the corrosion resistance.